In a fermentation process adapted to produce bio ethanol, an initial processing of organic material is often required before fermentation. Often such processing has different aims such as soaking (e.g. to remove silicates, salts and mineral elements such as stones, gravel, sand and clay and/or to raise the water content), cutting, oxidizing, dewatering of the organic material and these are carried out sequentially. Thus, seen in overall reference frame, the organic material must be made susceptible to fermentation.
Particular important aspects pertaining to rendering organic material susceptible to fermentation are soaking, cutting and/or washing of the organic material. Furthermore, other aspects relates to treatment of organic material treating the material chemically and/or enzymatically. Such aspect may of course being combined with soaking, cutting and/or washing.
Soaking, in the present context, preferably means that the organic material that typically are considered to be dry (with reference to a desired liquid content) needs to soak fluid, preferably being water, such as tap water. Soaking may also be used to release and/or dissolve contaminating matter. Dry material may in some instances also be referred to as unsoaked material.
Cutting, in the present context, preferably means that the organic material is cut into pieces, such as into smaller pieces than its initial size (before being cut).
Washing, in the present context, preferably means that contaminating matter is separated off from the organic material, typically by firstly being released by and/or dissolved in the liquid and secondly separated out. The contaminating matter may be stones, gravel, metal particles, silicates, salts, mineral elements in general, sand, clay or combinations thereof. Often the contaminating matter is particulate matter and is often located on the surface of the matter.
US 2008/0054108 discloses a pulper having a tank for receiving materials to be shredded. A rotor is fixed to the rotating output of a drive and the rotor comprising an annular rotatable hub and a plurality vanes projecting generally axially from the hub. The vanes have a side edge facing an axial direction and a plurality of teeth is provided on the side edge of the vanes for providing a rapid shredding of material with a reduced energy requirement.
U.S. Pat. No. 6,234,415 discloses a pulper that includes a rotor mounted in a tube adjacent to a screening plate having holes. The rotor includes helical vanes whose diameter decreases towards the outer end of the rotor. The rotor vanes carry in the vicinity of the screening plate a radially and outwardly projecting shoulder-like element. The element forms a pressure-generating and sub-pressure-generating device which exerts an alternating effect on the pulp as the rotor rotates, therewith counteracting clogging of the holes in the screening plates.
Both these devices resides in that the flow in the tank comprises recirculation in the tank of the liquid present in the tank, which makes retention time of the material to be pulped non-controllable. The un-controllable retention time is not the primary concern in pulping, where the size distribution of the shredded pulp is the crucial parameter. Therefore the above mentioned documents also discloses pulpers, where recirculation is utilized to ensure that all pulp leaving the pulping chamber is less than a size defined by filtering and where recirculation is used to avoid clogging of the filter.
The disclosed pulpers may be workable for pulping purposes, the flow pattern includes internal recirculation so that the material may or may not get in contact with the rotor a number of times whereby the material contained in a liquid in the pulper consist of material having a divers size distribution that may result in depositing which in turn may result in e.g. clogging. Furthermore, the retention time of the material in the liquid is considered non-controllable at least for the reason of recirculation.
A further issue pertaining to such recirculation is that the retention time of the material in the liquid may become unknown and non-controllable. This may become a problem if, for instance, soaking to a certain level (water content in material) is aimed at as one of the parameters governing the soaking process is the retention time. This may in particular become an issue when dissolving of minerals such as salts is aimed at.
A particular issue pertains to have the material to be treated assimilated in a liquid. Often the material to be treated has a considerably lower density than that of the liquid and in such cases that material tends float as “lid” on an upper surface of liquid rendering it very difficult to soak the material. Especially when dealing with very hydrophobic materials such as cereal straw, corn waste materials, sawdust, rice waste materials, wood chips, energy cane, sorghum, miscanthus grass, switchgrass etc.
A still further issue pertains to the destructive nature of contaminating particles such as stone and metal pieces may have on cutting edge.
Thus, an object of the present invention is to provide an apparatus and method at least mitigating some or more of the problems pertaining to the know apparatus and methods.
A further and in many instances important object of the invention is to render initially dry material pumpable, whereby the material may be pumped towards, and used as a hydraulic sealing in, a downstream process system.